Flamenco-dancing molecule may lead to better sunscreen

A molecule that protects plants from overexposure to harmful sunlight thanks to its flamenco-style twist could form the basis for a new longer-lasting sunscreen, researchers report.

New research on the green molecule reveals that it absorbs ultraviolet light and then disperses it in a “flamenco-style” dance, making it ideal for use as a UV filter in sunscreens.

The molecule is among a small number of suitable substances that are effective in absorbing light in the ultraviolet A (UVA) region of wavelengths. This opens up the possibility of developing a naturally-derived and eco-friendly sunscreen that protects against the full range of harmful wavelengths of light from the sun.

A better UV filter?

The UV filters in a sunscreen are the ingredients that predominantly provide protection from the sun’s rays. In addition to UV filters, sunscreens will typically also include:

• Emollients, used for moisturizing and lubricating the skin
• Thickening agents
• Emulsifiers to bind all the ingredients
• Water
• Other components that improve aesthetics, water resistance, etc.

The researchers tested a molecule called diethyl sinapate, a close mimic to a molecule commonly found in the leaves of plants that is responsible for protecting them from overexposure to UV light while they absorb visible light for photosynthesis.

The researchers first exposed the molecule to a number of different solvents to determine whether that had any impact on its (principally) light absorbing behavior. They then deposited a sample of the molecule on an industry standard human skin mimic where different wavelengths of UV light irradiated it.

Researchers then used the state-of-the-art laser facilities at the Warwick Centre for Ultrafast Spectroscopy to take images of the molecule at extremely high speeds, to observe what happens to the light’s energy when it’s absorbed in the molecule in the very early stages (millionths of millionths of a second).

The team also used other techniques to establish longer term (many hours) properties of diethyl sinapate, such as endocrine disruption activity and antioxidant potential.

What makes a good sunscreen?

“A really good sunscreen absorbs light and converts it to harmless heat. A bad sunscreen is one that absorbs light and then, for example, breaks down, potentially inducing other chemistry that you don’t want. Diethyl sinapate generates lots of heat, and that’s really crucial,” says Vasilios Stavros, professor in the chemistry department at the University of Warwick.

When irradiated, the molecule absorbs light and goes into an excited state but that energy then has to be disposed of somehow. The researchers observed that it does a kind of molecular “dance” a mere 10 picoseconds (ten millionths of a millionth of a second) long: a twist in a similar fashion to the filigranas and floreos hand movements of flamenco dancers.

That causes it to come back to its original ground state and convert that energy into vibrational energy, or heat.

It is this “flamenco dance” that gives the molecule its long-lasting qualities. When the scientists bombarded the molecule with UVA light they found that it degraded only 3% over two hours, compared to the industry requirement of 30%.

“We have shown that by studying the molecular dance on such a short time-scale, the information that you gain can have tremendous repercussions on how you design future sunscreens,” says Michael Horbury, who was a postgraduate research fellow at the University Warwick and is now at the University of Leeds.

“The next step would be to test it on human skin, then to mix it with other ingredients that you find in a sunscreen to see how those affect its characteristics,” says Emily Holt, a PhD student in the chemistry department.

“Amidst escalating concerns about their impact on human toxicity (e.g. endocrine disruption) and ecotoxicity (e.g. coral bleaching), developing new UV filters is essential,” Stavros says. “We have demonstrated that a highly attractive avenue is ‘nature-inspired’ UV filters, which provide a front-line defense against skin cancer and premature skin aging.”

Additional coauthors from the University of Warwick and AgroParisTech in France contributed to the work, which appears in Nature Communications.

Source: University of Warwick

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